In the beginning there was the retail prices index (RPI), appearing in embryonic form in 1914, with a fully fledged version in 1947.

For measuring inflation before 1914 the Office for National Statistics has a yardstick that goes back to 1750 based on sources including the cost of wheat, account books for alms houses and naval purchasing records.

The all-items RPI stood the test of time until the 1970s, when inflation took off, peaking at 27% in 1975. Thereafter, governments looked for alternative ways of calculating the cost of living. The first was RPI excluding mortgage interest payments - RPI(X) - in the mid-1970s. The thinking was that when policy makers put up interest rates to combat inflation, the immediate impact of the move was to push up the all-items RPI, adding to the risks of a wage-price spiral.

Next came the tax and prices index (TPI), brought in by Mrs Thatcher's first government, a measure of the increase that workers need to maintain their living standards after prices and tax changes are taken into account.

From 1987 RPI, RPI(X) and TPI were joined by RPI(Y). This measure excluded mortgage interest and a range of indirect taxes - currently council tax, VAT, excise duties, insurance tax and air passenger duty.

When Norman Lamont announced the first inflation target in 1992, he chose RPI(X), which remained the benchmark until 2003, when the Bank of England was told to target the consumer prices index (CPI) - an internationally agreed measure that excludes all owner-occupied housing costs.

So is that it? Not quite. The Rossi index, named after Tory minister Hugh Rossi, uprates benefits based on the September increase in the all-items RPI, excluding rent, mortgage interest, council tax and housing depreciation.